1. Field of the Invention
This invention relates to a photocurable composition which is developable with an aqueous alkaline solution and is applicable particularly advantageously to the formation of a conductor circuit pattern, a barrier rib pattern, a dielectric pattern, a fluorescent pattern, and a black matrix on the front and the back substrate of a plasma display panel, and applicable also to the formation of an electric conductor, a resister, and a dielectric element for use in a fluorescent display tube and electronic parts. This invention also relates to such calcined patterns as a conductor pattern, a vitreous dielectric pattern, and a fluorescent pattern which are obtained by the use of the photocurable composition.
2. Description of the Prior Art
A plasma display panel (hereinafter abbreviated as "PDP") is a planar display for exhibiting pictures and pieces of information by utilizing the light emitted by plasma discharge. It is classified under the DC type and the AC type according to the structure of panel and the mode of driving. The principle of color display by the PDP consists in generating plasma discharge in cells (discharge spaces) between two opposed electrodes severally formed on a front glass substrate and a back glass substrate separated by intervening ribs (barriers), and exciting the phosphor formed on the inner surface of the back glass substrate with the ultraviolet light generated by the discharge of such a gas as He or Xe sealed in the cells thereby inducing generation of visible lights of three primary colors. The cells in the DC type PDP are divided by the component ribs of a lattice, whereas those in the AC type PDP are divided by the ribs which are parallelly arranged on the face of the substrate. In either case, the cells are divided by ribs.
FIG. 1 illustrates a typical construction of the planar discharge type PDP using a three-electrode structure for full color display. On the lower face of a front glass substrate 1, many pairs of display electrodes 2a, 2b each comprising a transparent electrode 3a or 3b intended for discharge and a bus electrode 4a or 4b intended for lowering the line resistance of the transparent electrode are formed. On the display electrodes 2a, 2b, a transparent dielectric layer 5 (low melting glass) for accumulating electric charge is formed by printing and calcination. A protective layer (MgO) 6 is formed thereon by vacuum deposition. The protective layer 6 assumes the role of protecting the display electrodes and maintaining the state of discharge.
On a back glass substrate 7, ribs (barriers) 8 shaped like stripes and adapted to partition discharge spaces and address electrodes (data electrodes) 9 severally disposed in the discharge spaces are formed with prescribed pitches. On the inner faces of discharge spaces, fluorescent films of the three colors, i.e. red (10a), green (10b), and blue (10c), are laid out regularly. In the full color display, the fluorescent films of the three primary colors of red, green, and blue mentioned above jointly form one picture element.
The PDP described above is called a "planar discharge system" because an AC pulse voltage is applied between the pair of display electrodes 2a, 2b to induce discharge between the electrodes on one and the same substrate. It has a construction such that the ultraviolet light generated by discharge excites the fluorescent films 10a, 10b, and 10c of the back substrate 7 and the visible light consequently generated is seen through the transparent electrodes 3a, 3b of the front substrate 1 (reflection type).
In recent years, the front substrate and back substrate of the PDP, the electrode circuit substrate of a printed circuit board, and the like have been witnessing steady advance of the patterns formed thereon toward higher fineness. In consequence of this trend, the desirability of improving the technique for the formation of such patterns has been finding growing approval. Particularly, the plasma display panels have been undergoing conspicuous technological innovations devoted to enlarging size and enhancing resolution. The manufacturers of plasma display panels have recently succeeded in commercializing such panels of the 50-inch class and have been continuing an effort to produce such panels in a larger size with higher resolution.
Heretofore, the conductor patterns and dielectric patterns in plasma display panels, fluorescent display tubes, electronic parts, etc. have been generally formed by the screen printing process which uses an electroconductive paste or a glass paste containing a very large amount of metal powder or glass powder. The formation of such patterns by the screen printing process, however, entails such problems as requiring skill on the part of workers, exposing the layer of fresh paint deposited by printing to the possibility of sustaining blurs or blots, degrading the accuracy of registration of printed patterns due to expansion and contraction of the screen, and jagging the formed pattern due to the contact with the screen mesh. Thus, the screen printing process produces required patterns only with a poor yield and incurs difficulty in coping with the trend of patterns toward higher fineness and the trend of plasma display panels toward enlargement of size. In the circumstances, the desirability of developing a pattern processing material which is capable of more stably coping with the demand for patterns of higher fineness and for panels of larger size has been finding recognition.
As a prospective alternative for the screen printing process, therefore, the photolithographic process has been proposed in published Japanese Patent Application, KOKAI (Early Publication) No. (hereinafter referred to briefly as "JP-A-") 1-296,534, JP-A-2-165,538, and JP-A-5-342,992, for example. The photolithographic process forms a pattern by applying an ultraviolet-curable glass paste to an insulating substrate and exposing and developing the coating of paste. It is generally known to use a macromolecular compound containing carboxyl groups for the purpose of rendering a given composition developable with an aqueous alkaline solution. When the macromolecular compound containing carboxyl groups is made to incorporate such a fine basic inorganic powder as glass frit, however, the paste consequently obtained acquires too inferior viscosity stability to fit practical use. Specifically, the glass paste composition of such inferior viscosity stability entails deterioration of the operational efficiency of coating work and degradation of the developing properties of the applied coating in consequence of such phenomena as gelation and decline of flowability and consequently brings the problem of affording no sufficient allowance in work.